Fosun International Ltd.’s health-care business and Shanghai Pharmaceuticals Holding Co. are among bidders for a stake in U.S. specialty drugmaker Arbor Pharmaceuticals LLC, according to people with knowledge of the matter.

Fosun and Shanghai Pharma are among potential acquirers competing to buy a stake of at least 20 percent to 30 percent, the people said, asking not to be identified because the matter is confidential. The holding in the Atlanta-based drugmaker, backed by KKR & Co., could fetch around $600 million to $700 million, the people said.